This invention relates to the recovery of energy from geothermal brines and other hot water sources, and is particularly concerned with a process and system of the aforementioned type, employing direct contact heat exchange between the hot brine or hot water feed, and a working fluid, and employing a plurality of separate stages in which the hot brine or hot water is intimately mixed with the working fluid, and the two fluids thereafter separated in each stage, whereby the heat from the hot brine or hot water is transferred in increments to the working fluid to raise the temperature thereof.
Direct contact heat exchange (DCHE) has been proposed as a method for recovering thermal energy from scale depositing geothermal fluids, e.g. hot geothermal brine. Thus, U.S. Pat. No. 3,988,895 to Sheinbaum discloses power generation from hot brines by passing a hot fluid containing salt such as geothermal brine, in direct contact heat exchange relation with a working fluid such as isobutene.
In the copending application Ser. No. 589,068, filed June 23, 1975, by Samuel G. Woinsky, there is described a process and system for recovery of energy from geothermal brine and other hot water sources, which comprises cooling the brine or hot water source in direct contact heat exchange relation with a working fluid in a direct contact heat transfer column, and having as an important feature the operation of the heat transfer column at or above the critical pressure of the working fluid. In the copending application Ser. No. 611,310, filed June 23, 1975, now U.S. Pat. No. 4,089,175, by Samuel G. Woinsky, there is described a similar process and system as in the above-mentioned application, and having as an important feature operation of the heat transfer column at a pressure below the critical pressure of the working fluid.
The direct contact heat exchangers of the prior art as exemplified above are generally in the form of the sieve-tray type, wherein the liquid brine enters at the top of the column and falls through a series of trays, with the working fluid travelling upward and mixing with the hot brine. The working fluid is then extracted at the top, e.g. as a vapor, where the temperature differences are such that the working fluid passes through its boiling zone. Another type of prior art direct contact heat exchanger employed is of the packed column type wherein mixing of the hot brine and working fluid and countercurrent flow thereof through the column are achieved by passage of the fluids through a mesh or other type of packing.
Other related prior art patents include the Morris U.S. Pat. No. 1,905,185 and the Fricke U.S. Pat. No. 3,164,957, which disclose liquid-liquid direct contact heat exchange, wherein two liquids are permitted to mix for transfer of heat from one liquid to the other, followed by separation of the fluids due to differences in density.
It is accordingly an object of the present invention to provide a process and system for direct contact countercurrent heat exchange between a hot water containing fluid such as geothermal brine, and an immiscible working fluid, employing a plurality of self-contained stages, in each stage of which the working fluid is incrementally heated by the hot aqueous fluid. Another object of the invention is to provide a process and system of the above type, incorporating in each stage mixing and settling of the fluids passing in countercurrent relation to each other. A still further object is the provision of a direct contact heat exchange process and system as described above, having certain advantages over the prior art direct contact heat exchange systems, including safety, reliability and overall economy of operation.